100-4 Tracking Sediment Provenance to Constrain the Tectonic Evolution of the Neoproterozoic Western Margin of the Congo Craton, NW Namibia

Session: Snowballs, Unconformities, BIFs and Beyond: Navigating the Neoproterozoic Rock and Climate Records Using Geochronology

Presenting Author:

Isabel Koran

Authors:

Koran, Isabel¹, Renger, Ellery Muire², Macdonald, Francis A.³, Tasistro-Hart, Adrian⁴, Nelson, Lyle Lee⁵, Rose, Catherine⁶, Kylander-Clark, Andrew⁷

(1) UC Berkeley, Berkeley, CA, USA, (2) UC Berkeley, Berkeley, CA, USA, (3) UC Berkeley, Berkeley, CA, USA, (4) UC Berkeley, Berkeley, CA, USA, (5) MIT, Cambridge, MA, USA, (6) University of St Andrews, St Andrews, United Kingdom, (7) UC Santa Barbara, Santa Barbara, CA, USA,

Abstract:

The western margin of the Congo craton hosts a Cryogenian carbonate-dominated sequence with interstratified diamictite that has been central to interpretations of Snowball Earth. Yet uncertainty persists regarding the tectonic setting(s) and subsidence that accommodated these strata, in part due to ambiguity in age models and stratigraphic correlations between distal margin parautochthonous and allochthonous sections to the west and platformal autochthonous sections to the east. In one model, a passive margin endured until middle-Ediacaran closure of the Adamastor Ocean basin to the west, culminating in the Kaoko Orogen. Alternatively, Tonian to early Cryogenian rifting preceded a short-lived passive margin and arc-continent collision in middle Cryogenian time—or the entire Cryogenian succession formed in a back-arc setting. In the latter two scenarios, Sturtian and/or Marinoan glacial deposits were deposited on a collisional margin. These tectonic models make specific predictions regarding the distribution and timing of sediment sources to the basin, which we test using a combination of U-Pb LA-ICPMS detrital zircon geochronological data, new mapping, and stratigraphy across multiple northeast-southwest transects (modern coordinates) in northwest Namibia. Classic carbonate platform strata of the Otavi Group are correlated to slope- and basin-facies equivalents using Sturtian and Marinoan glaciogenic deposits, supported by sequence stratigraphy and chemostratigraphic data. Cryogenian deposits between the Sturtian Chuos Formation and the Marinoan Ghaub Formation capture a distinct shift in provenance, consistent with sediments derived from allocthonous igneous sources in the Coastal Terrane, and thus consistent with a tectonic transition to a collisional western margin by middle Cryogenian time.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7289

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